This invention concerns field of the Invention rock or similar materials in surface or underground mining operations where bore holes are charged with explosives and detonators.
Such blasting technologies are known from experience respectively from European patent application 0 147 688 A2 and the German disclosure document DE 197 21 839 A1.
It was discovered that for such blasting technologies the applied detonating agents have a decisive influence on the quality of the blast. Here discrimination is made between electric, nonelectric and electronic detonators.
Electric detonators feature a pyrotechnical compound together with a filament, which is heated by electric energy. A non-electric detonator mostly consists of a thin plastic hose containing explosives. This hose is ignited by an impact, respectively a fuse cap. The plastic hose then ignites the pyrotechnical delay composition in the detonator.
Electronic detonators do not need a pyrotechnical compound. They get the ignition energy from an energy-storing device like e.g. a capacitor. This capacitor heats a filament or any other device, which can be heated by electricity. Basically this is already described in the European document and the German disclosure document DE 197 21 839 A1. The blasting technologies known until now are not fully convincing. Because until now only a mutual support of neighboring bore holes can be achieved in the same row of bore holes in the sense of intensifying the disintegration of the rock masses to be blasted. In other words, the energy of a subsequent shot cannot or can only insufficiently be coupled to the energy of the preceding shot. Furthermore, such phenomena could until now only be observed by chance and they could not be predicted. This invention is supposed to improve this situation altogether.
This invention is based on the technical problem of further developing such a technology in a way that a focused mutual impact of the shock waves coming from the individual bore holes can be achieved.
To solve this task it is proposed by this invention utilizing a technology for blasting rock or similar material that electronic detonators and their respective time delays are programmed in consideration of the mineralogical and geological environment and the seismic velocities resulting thereof and the respective firing patterns. In most cases, an electronic detonator with a continuously, variable programmable moment of ignition is applied. With such electronic detonators, it is possible for the first time to freely program variable delay intervals from one detonator to the other, respectively from bore hole to bore hole. This is basically because electronic detonators, as mentioned before, do not have a pyrotechnical firing compound. Rather, they have an electronic switch which is connected after the battery (respectively the capacitor) that allows the electric energy to flow into the ignition device of the detonator when switched on. This electronic switch, specifically a switching transistor, can be correspondingly controlled by a data control part inclusive a control unitxe2x80x94i.e., actually a computer in form of a microchip. This design enables the electronic detonator to be accurately detonated with accuracy of one millisecond.
In order to increase the explosive effect, the invention proposes that shock wave fronts coming from the respective bore holes interfere with each other in order to open the structure of the rock to be blasted. So there is a wave interference of the shock waves and a wave interference of the seismic waves. This colliding and inter-reacting of various multiple wave fronts leads to the desired fracture of the structure, i.e. the connections in the respective solids are loosened from the excitation from the outside.
Shock waves are generally understood as being three-dimensionally spreading, abrupt and consistent changes of density, pressure and/or temperature of the material to be blasted. Such a shock wave develops when a huge amount of energy is suddenly releasedxe2x80x94such as by an explosion or the ignition of an explosive charge in a bore hole with the help of the (electronic) detonator. The leading edge of this spreading of energy represents a shock wave. The propagation velocity of this shock wave can be a multiple of the sonic velocity of the surrounding medium and mainly travels at supersonic speed.
Within the framework of this particular invention, seismic waves shall not only be regarded as shock waves, or tremor waves, but any kind of vibration waves which travel away from an epicenter (mostly a bore hole with an explosive charge) in the rock to be blasted.
As the propagation velocity of the respective seismic wavexe2x80x94apart from the so-called pressure waves or shock wavesxe2x80x94depends on the material and its ability to be compressed, there is a certain and characteristic propagation speed at a given density and temperature, the sonic speed. This represents a parameter depending on the material and can, in case of rock mass, amount to more than 1,000 m/sec or even several 1,000 m/sec.
The field of elastic deformation and the given compressibility of the rock, which conducts the seismic wave or the sound wave are of concern if only waves with small amplitude are excited in the rock. If there is a bigger and sudden excitation, then the shock waves, or tremor waves are created. They have the favorable effect that at least in the area of the blast the atoms in the solid lattice are not elastically deformed against each other anymore, so their connections break up. The solid structure is destroyed (for the most part).
As the shock wave velocity is mostly supersonic, this speed amounts to Mach 1 and more. For the increase of the explosive effect, the firing sequence is arranged in such a way that the shock waves from the individual bore holes and the seismic waves, particularly sound waves, overlap and interfere [amplify]. The shock wave system in the area of the blast is being compressed. This means that wave amplitudes are created, which result from the (positive) overlapping of individual shock waves. This can be controlled with programmable delays in such a way that, altogether a shock wave system is created by the wave velocities of which propagate supersonically, i.e. their speed is above mach 1.
The procedure here is as follows. The sequence of ignition is arranged in such a way that the accumulated sum of the delay times is smaller than the traveling time of the sonic speed resulting from the rock to be blasted. In other words, the delays between the first bore hole to be fired and the last bore hole to be fired are chosen in such a way that the velocity of the ignition (horizontal ignition velocity) is equal to or faster than the sonic speed in the material to be blasted (rock velocity).
By this, it is possible to create calculated delay models of the individual ignition sequences, so called firing patterns. The choice of the individual delays determines the fragmentation of the blasted material (pile of debris). It even determines the distribution respectively of the accumulation of the material in the area of the blast. This is because individual seismic waves interfere in such a way that, at certain spatially exactly defined spots, wave interference peaks happen, leading to a particularly extensive fracture of the rock masses to be blasted in this particular area. But the wave interference minima, on the other hand, correspond in such a way that only a limited fracture of the rock is achieved.
But as the seismic waves spread from the respective bore hole with the sonic speed through the respective rock, the wave patterns move and hence the wave interference peaks and minima travel as well. This can either happen in the shape of counteracting or paralelly running waves and/or shock waves.
Thus, it can be observed as the overall result, that there are compression effects by the described wave collisions resulting from the multiple oscillations or flow of the respective wave fronts through the rock masses. Due to the specific sequence of ignition of the explosives charges detonating one after the other, it results in an almost continuous process of creating a seismic wave interference, or shock wave, with the character of a constant flow. As a result, the rock masses in the blasted area are transformed into a mineral mixture with a colloidal-mechanical cohesion.
In the blasted area, the shock wave""s or the seismic wave created by the blast has a particularly high frequency. This high-frequency shock wave approaches the sonic speed of the rock to be blasted and its natural frequency, depending on the distance from the source of excitation.
The shock effect described previously comes as a result of an excitation by impulse of the rock due to the detonation of the explosives in the bore hole, which corresponds to the ultra-high frequencies in the range of 400 Hz up to several kHz.
The frequency and the amplitude of these shock waves are able to excite the solid structure of the rock in the close range area (blast area) to such an extent that this leads to a partial or complete disintegration of the solid. Consequently, the close range area determines the actual blast areas where the seismic wave, or the shock wave, spreads concentrically from the center of the source of excitation, i.e. the explosive charge or the bore hole.
It is furthermore possible in the frame of this invention to place an electronic detonator at the bottom of the bore hole and a second one on top of the charge column at the mouth of the bore hole. These detonators can now be programmed to exactly the same delay, or different delays such that two shock wave fronts, or detonation fronts, are created, which collide in the middle of the charge column. This leads to a doubling of the velocity of detonation and to an increased conversion of the charge column due to the colliding shock wave fronts.
As previously described, the freely programmable delays and the resulting ignition velocity directly depend on the sonic speed in the rock to be blasted. This means, in other words, that the ignition velocity has to be synchronized with the physical velocities (particularly the speed of sound).
To achieve this, the invention proposes that the seismic velocity, respectively the sonic speed in the rock to be blasted, be determined in advance by measurement and/or by calculation, before the firing pattern is developed. This can be done by, e.g., having a look at the boring log, which provides a fairly precise picture of the rock formation. The seismic velocities to be expected can be discerned from the boring log and the necessary horizontal ignition velocity (velocity of the ignition from the first bore hole to be detonated to the last bore hole to be detonated) can be determined.
Basically, it is also possible to use bore holes at the back edge of the area to be blasted to create counteracting shock waves, respectively seismic waves. Thus, it is possible to define the blasted area in a way which was not believed possible with the current state of the art. This is made possible by the freely programmable firing pattern with its varying delays from one blast to the other.
In addition to the seismic wave, or shock wave, the blasted rock is further fragmented by a gas pressure wave, which follows after the detonation of the explosives. This one is produced with a slower propagation velocity, compared to that of the seismic wave and is called the detonation shock wave velocity. This gas pressure wave amplifies the explosive effect of the shock wave by penetrating the cracks in the rock, which were created by the shock wave.
In this context, the invention also demands that the shock wave velocity, or the seismic velocity, and the detonation shock wave velocity are synchronized as they are subsonic.
This synchronization of the shock wave velocities and the detonation shock wave velocity can be traced back to the fact that the detonation shock wave velocity depends on the structure and the cohesive strength of the material to be blasted. In general it can be said that the smaller the grain size of the pile of debris after the blast, the greater the detonation""s shock wave velocity. This is a result of the wave interferences of the shock waves.
It is also possible within the framework of this invention not only to discriminate between pre-split blasts and production blasts, but also to synchronize them. Pre-split rows are certain rows of bore holes at the back edge of the drilling pattern. These pre-split rows are meant to form the boundary of the actual blast area and shall, among other things, create an even and sturdy bench wall. So it is possible that such pre-split holes surround the entire blast area or at least limit one side where the straight and sturdy bench wall is desired. The detonation of the charges in the pre-split holes is called the pre-split blast. In contrast to this, production blasts are meant to loosen the material in the actual blast area.
By the precise programming of the delays of the applied electronic detonators, it is possible to synchronize the pre-split blast and the production blast. In general, the production blast is ignited slightly ahead of the pre-split blast. So the seismic waves from the bore holes of the production blast create wave interferences with the seismic waves of the pre-split holes.
It is assumed that the directions of propagation are more or less contrary and hence there is a wave collision in the center of the blasted area. This effect is further increased by the seismic waves from the production bore holes which were ignited first and which are reflected from the exposed face.
In any case, the synchronization between the pre-split blast and the production blast is carried out in such a way that the vibrations in the blast area are neutralized, which, in the ideal case, would mean that there are almost no vibrations in the blasted area and in the bench wall.
It is also in the scope of this invention to temporarily combine individual bore hole blasts or rows to a bore hole row respectively pre-split bore hole row to be simultaneously ignited. Also, individual production bore holes can be linked and then ignited together. This is basically true for all bore holes no matter whether they are production holes or pre-split holes. Consequently bore hole patterns, ignition sequences, or firing patterns, and corresponding ignition delays can be freely programmed between each other.
The pre-split technology described here enables a clear definition of the blast area in sensitive and even in inhabited areas. Here the pre-split row represents a reflection face for the production blast. A firing pattern with several rows of bore holes and in which the detonators are ignited following a firing pattern which overlaps the individual rows or is in a triangular or circular configuration is also part of the invention.
Electronic detonators allow total control of the programmed ignition delays. This not only makes it possible to control the velocity of detonation of explosives, but also to manipulate the explosive effect in the respective bore holes. This has already been described with the application of two detonators per charge column (one on the bottom plus one on the surface).
An additional advantage of the invention is that, with the design of the firing pattern or the combination of the ignitions amongst each other and the programming of those, a new level of effectiveness is created. Now the result of the blast can not only be influenced by the geometry of the bore hole and the applied explosives but also by the described programming and design of the firing sequence.
From the vibrations outside the area of the blast information for damage control can be gained. They also provide important information for succeeding blasts. The seismic waves also provide information about the sonic speed in the material for succeeding blasts. Actually the seismic waves propagating themselves in the long distance are showing naturally excellent base values for succeeding blasts to be performed at this place (especially the sound velocity in the affiliated material). These seismically obtained values are of course useful for the determination of the ignition velocitiesxe2x80x94particularly the so-called horizontal ignition velocity as described before. Here it is imperative that the last bore hole to be ignited must detonate before the shock wave of the first bore hole to be detonated arrives.
Thus, with the application of the newly described procedure, the amount of explosives can be considerably reduced as the wave interferences of the seismic waves, or shock waves, deliberately and properly utilized by the new procedure. Additionally, fewer bore holes are needed. Furthermore, the invention makes it possible to clearly define the area of the blast by producing counteracting shock waves at the back edge of the blast, thus defining a tightly enclosed blast area and reducing, to a minimum, the encroachment of the blasts into the environment outside the area.
In contrast to the current state of the art, and when short distances between the bore holes are concerned, the so-called sympathetic transmission from one bore hole to the other can be avoided. This means that there is absolutely no compression of an explosive charge in the neighboring bore hole by the shock wave produced when firing the first bore hole. Thus, false ignitions are excluded as may happen with other ignition technologies because the charge column of a bore hole has already been detonated before the seismic wave or the shock wave of the neighboring bore hole is felt. So no damage is caused to the charge column before it is detonated.
A further consequence of this technology is that the blasting operations themselves become considerably much safer and easier. Basically the observation of additional safety standards, as laid down in the already mentioned German disclosure document 197 21 839 A1 can be taken as granted.